Patrice, thanks for filing the bug report. I was just looking at that bug myself. The definition of g_tclextlib at line 41 is in new code added since the version 4.2.2 that's in Buster.
I'm NOT a Tcl programmer or Modules guru. But is "prefix" something that should be compiled into the modules at build time, or initialized in /etc/environment-modules/siteconfig.tcl, or maybe in a file /etc/environment-modules/rc? As a workaround I edited modulecmd.tcl to replace "${prefix}" with "/usr" at line 41. That allows /usr/share/modules/init/bash to complete successfully and define function "module" correctly. Hope this helps. -- James Ronald Lovell <ron163...@gmail.com> Huntsville, AL, USA